Heretofore, a vane type vacuum pump provided with an escaping groove for allowing a lubricating oil to escape at the time of the reverse rotation of the vane is publicly known (Patent document No. 1).
That is, the vane type vacuum pump includes a housing provided with a nearly circular pump chamber, side plates sealing opposing end surfaces of this housing, a rotor rotating at a position eccentric to a center of the pump chamber, a vane reciprocating along a groove formed in the diameter direction of the rotor and rotating while partitioning the pump chamber into a plurality of spaces, and an escaping groove provided in the vicinity of an air intake passage through which the air is sucked into the pump chamber and communicating a space on the front side and a space on the back side of the rotational direction of the vane at the time of the reverse rotation of the vane, thereby allowing the lubricating oil to escape into the space on the back side from the space on the front side.
At the reverse rotation time in which the rotor rotates in the direction opposite to a normal direction, a compression effect is generated in the vicinity of the air intake passage. The vane type vacuum pump is generally driven by the engine of an automobile, and therefore, when the engine is reversely rotated, the rotor and the vane of the vane type vacuum pump are also reversely rotated. More specifically, the compression action occurs in the case where manual transmission car is stopped in an upward slope, and in a state in which the engine shuts down, the wheels and the engine are connected through a clutch, and in this state, the wheels pull back in the slope.
Now, at the engine shutdown time, though a stored amount of the lubricating oil is different depending on a mounted state of the vane type vacuum pump to the vehicle and a condition such as configuration and the like of the feeding passage of the lubricating oil to the pump chamber, it is known that since the inside of the pump chamber is maintained in a negative pressure state, the required volume of the lubricating oil is sucked and stored inside the pump chamber. When the vane is reversely rotated in this state, supposing that the escaping groove is not provided, because the lubricating oil is a non-compressible liquid, the pressure in the vicinity of the air intake passage becomes extremely high, and there arise problems that the vane is broken or a check valve is broken when the check valve allowing a flow of the air to the pump chamber is provided in the middle of the air intake passage.
Since the escaping groove can communicate the space on the front side and the space on the back side of the rotational direction of the vane at the time of the reverse rotation of the vane in the vicinity of the air intake passage, the lubricating oil can be allowed to escape from the space on the front side to the space on the back side by this escaping groove, and this can prevent the breakage of the vane and the check valve.    [Patent document No. 1] Japanese Laid-Open Patent Application No. 2000-205159